Enols of aldehydes in the peroxidase/oxidase-promoted generation of excited triplet species.

General (acid and base) or specific (fluoride ion) catalysis generates the enol of isobutanal and propanal from the corresponding trimethylsilyl enol ethers. The enols are directly rapidly oxidized by peroxidase (acting as an oxidase) to triplet acetone or triplet acetaldehyde, respectively, and formic acid. Due to the faster rate of reaction and the absence of quenching by excess aldehyde, the excited carbonyl emits more strongly than when the aldehyde itself is the substrate. With both enols the emission is pure phosphorescence. Both triplet acetone and triplet acetaldehyde are generated within the enzyme, as shown by the different quenching by D- and L-tryptophan, and are somewhat protected from oxygen quenching, as attested by the very fact that phosphorescence is observed. The use of enol precursors as substrates opens wide possibilities for photochemical investigations in the absence of light over a much broader range of experimental conditions.